The present invention is directed to a wafer handling robot. In particular, it relates to a wafer handling robot which performs the task of centering and notch or flat finding, commonly referred to as pre-alignment.
Wafers used in the semiconductor industry are disks of semiconductor material with a generally circular shape having a straight edge referred to as the "flat"or "notch"interrupting the circular edge at one location. Some wafers have two distinct flats or notches interrupting the circular edge. Typically, wafers are transported and handled by wafer handling robots, so as to minimize contact of the wafer with contaminants. When handling a wafer, it is important to know where the center of the wafer is and where the flat of the wafer is located in relation to the components of the handling apparatus. This information, acquired in a step commonly called "pre-alignment,"allows the wafer handling robot to properly place the wafer in a desired location. Pre-aligning the wafer also enables the wafer handling robot to avoid bringing the wafer into contact with any objects during transportation and placement of the wafer.
Such wafer handling robots are typically polar coordinate robots having three axes of movement along which the robot can operate. These axes include a vertical axis Z, a rotational axis theta and at least one radial axis R. In typical wafer handling robots, an extra moving element movable along at least one additional axis is necessary to perform the pre-alignment task. Thus, a second mechanism is necessary to perform pre-alignment of the wafer. The use of a second mechanism to perform pre-alignment of the wafer increases both the size and cost of the system, and can result in additional handling of the wafer which can result in the wafer coming into contact with increased amounts of contaminants.